concrete grades please
concrete grades please
(OP)
i would like to know how the different concrete grades relate to concrete mixes.for example what concrete mix do i use to achieve a concrete grade 25,as well as grade 15,25,30.
concrete mixes include 1:2:4, 1:3:6, etc
concrete mixes include 1:2:4, 1:3:6, etc





RE: concrete grades please
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: concrete grades please
around here we use class for our concrete such as
Class A - Min. Cement Content Lbs. Per Cu Yard 520, 3,000 psi shall be used for concrete structures, either reinforced or non-reinforced, and for concrete pavements.
Class B - Min. Cement Content Lbs. Per Cu Yard 470, 2,500 may be used for curbs, gutters and sidewalks.
Class C - Min. Cement Content Lbs. Per Cu Yard 420, 2,000 psi may be used for thrust blocks, encasements, fill or over-excavation, etc.
Class AA - Min. Cement Content Lbs. Per Cu Yard 600, 4,000 psi for structures as specified
RE: concrete grades please
RE: concrete grades please
RE: concrete grades please
RE: concrete grades please
What do you do when the supplier follows the perscriptive requirement and does not achieve the performance requirements?
Or what if he has to use more cement or a different aggregate to get the strength, but ends up with a change in other properties such as shrinkage, permeability, density (for lightweight concrete only), etc?
The minimum performance requirements strength, air content, slump, etc. and material standards (ASTM) are easy to verify and monitor. Once you begin to impose perscriptive requirements in addition to the performance requirements, the water gets cloudy and the specifier can incur more respomsibility. Approval of mix designs is perhaps a middle ground, since the contractor/supplier is making the sunmittal.
I have seen situations where it is impossible to satisfy both the performance and prescriptive requiremnts. ASTM C270 is a classic example, but this ASTM standard directly says to use or the other, but not both.
RE: concrete grades please
The Euronorm BS EN 206 and its UK counterpart BS8500, specify the grades along with the restrictions on mix design, minimum and maximum cement content, maximum water cement ratio, minimum aggregate size. Using this information along with required 7 and 28 day strengths the quarry will usually do the mix design. ie they do the calculations to work out exactly how much cement, sand aggregate and water goes into the mix, along with any admixtures required to meet the design parameters
You can have a number of different mixes which give the same concrete grade and meet the design requirements.
Concrete mixes batched by volume 1:2:4 etc are very rough and have no quality control attached to them. There is no way to guarantee a design strength and as such should never be used to structural concrete. They are fine for small quantities to set a kerb or haunch a manhole cover for example.
RE: concrete grades please
I believe the duel spec, strength and cement content, goes back to when the mix designs were provided by the local agency. Our local DOT just stopped providing the mix designs to contractors in the last two years.
RE: concrete grades please
RE: concrete grades please
RE: concrete grades please
RE: concrete grades please
RE: concrete grades please
RE: concrete grades please
the concrete grade actualy specifies the cube strenght in 28 days.grade 30(G30)means 30N/mm2 strenght whereas the concrete mix ratios stands for cement ratio to sand to coarse aggregate.but i still wonder if we can achieve such cube strenghts by merely following these mix ratios .
RE: concrete grades please
1 Newton (N)= 0.1019716 Kg force
1 Pascal = 0.1019716 Kg/m2= 1 N/m2
1 Megapascal = 101971.6 Kg/m2 = 0.1019716 kg/mm2 = 1 N/mm2
1 Megapascal = 145.0377 psi = 10.19716 kg/cm2
The usual requires of the concrete are:
So Strong structures:
30 Megapascal(N/mm2)=4351 psi = 305 kg/m2;generally 4500 psi
Strong structures:
25 MP (N/mm2) = 3625 psi = 255 kg/m2; generally 4000 psi
20 ,, = 2900 psi = 203 kg/m2; gen. 3000 psi
Blinding concrete or walkways:
15 ,, = 2175 psi = 152 kg/m2; gen. 2000 psi
If you have concerns how to meet the spcs strength, you must send the material samples to the soil lab. Have an advise from any of them. If you can proceed without that, try the best safety for so strong: 1:2:2 or 1:2:3 if sand's not so fine grains and gravel is angular shape
I hope it could help, good luck!
RE: concrete grades please